My gf of 6 years left me and I do not want to go on anymore

Hi everyone. I'm 35 and I've lost a lot of weight after college. My life has gotten a lot better afterwards. I met a girl online, and we started chatting and then dating, we had so much in common. I was a shy kid in school, in HS I had a group of friends, together we shared laughs and memories, we would party and do all kinds of things, even bullying each other and pranking each other. I had a lot of fun in high school but I never dated until college and I did not really have have any luck. I didn't lose hope. This girl and I have dated for 6 years, we would go on 2 trips a year, we have a dog and a cat, and she would always tell me how lucky she feels that we found each other and how lucky she feels to have a soulmate. She was the best thing that ever happened to me. But I failed to notice that the past 2 years she became more and more distant. She would help me with chores, cook for me, and go to the gym together. I started to notice that she started going to the gym more often and started wearing more revealing clothes. She met a guy at work and soon enough, she told me that she is in a relationship with him. I'm absolutely heartbroken, I haven't left my room or my house in 3 weeks. I wouldn't eat much if it wasn't for my dog bothering me. It got to the point where he eats my food because it's too late and I'm just sitting in bed staring at the wall. I do not have any family or friends. I lost my mom when I was 3 and I was raised in foster care, then group homes and then I was on my own. I did well through HS and got a scholarship, and I had a few friends in college but we all went our ways. I do not know how to go on. I know there is light at the end of the tunnel but it is just so dark and cold that I do not want to continue. I have been thinking of ending it.